One method of providing broadband communication services onboard moving vehicles (e.g., airplanes, trains, cars, buses, trucks, ships, etc.) is by communicating with a base station through RF transceivers on one or more earth satellites. For example, an antenna on the vehicle directed at the satellite may receive signals from the satellite. However, antennas externally mounted on vehicles moving in an ambient fluid (e.g., air) preferably have a low profile to minimize drag forces which slow vehicle motion and/or require extra motive power.
One approach (e.g., see earlier related application Ser. No. 10/546,264 referenced above) to achieving a low profile antenna is to use a plurality of arrayed antennas (including separately positioned sub-array components), each antenna being smaller (i.e., lower in profile) than a single antenna (or sub-array) with equivalent gain. A similar approach is described in U.S. Pat. No. 6,999,036 to Stoyanov et al. (the disclosure of which is hereby incorporated by reference) including the possibility of using electronic beam steering to supplement mechanical steering.
U.S. Pat. No. 5,678,171 to Toyama et al., the disclosure of which is hereby incorporated by reference, also describes use of a plurality of antenna arrays on an airplane. Using a plurality of antenna arrays rather than a single antenna, reduces the profile of the total antenna structure extending externally of the airplane for a given antenna gain. A similar approach is described in U.S. Pat. No. 4,679,051 to Yabu et al., the disclosure of which is hereby incorporated by reference.
U.S. Pat. No. 5,309,162 to Uematsu et al., the disclosure of which is hereby incorporated by reference, also describes use of two parallel antenna panels fixed with respect to each other but controllably rotatable together about azimuth and elevation axes. U.S. Pat. No. 6,657,589 to Wang et al., the disclosure of which is hereby incorporated by reference, also describes a low profile satellite antenna, which includes a pair of antenna assemblies.
Another approach used in the past to reduce antenna profile is to make a phased array antenna with an RF radiation pattern principal lobe beam direction not perpendicular (i.e., “tilted” at an acute angle) to the surface of the antenna array aperture. See, for example, the embodiments of FIGS. 6A-C in U.S. Pat. No. 6,999,036 to Stoyanov et al. noted above where electronic tilt is applied to each of plural antenna sub-arrays.
U.S. Pat. No. 6,259,415 to Kumpfbeck et al., the disclosure of which is hereby incorporated herein by reference, suggests a different approach, in which a single flat antenna panel (of arrayed elemental RF radiators) is used. In the Kumpfbeck antenna, the antenna beam is electronically fixed at an acute angle (e.g., 45°) relative to the antenna panel radiating surface. Thus, instead of requiring a 70° physical tilt of the antenna array panel (e.g., downward in elevation from a vertical orientation) in order to communicate with a satellite at a 20° elevation angle, a physical downward tilt of only 25° is sufficient.
U.S. Pat. No. 6,191,734 to Park et al., the disclosure of which is hereby incorporated by reference, describes an array of flat sub-array antenna panels, which have an electronic beam tilt control, such that instead of mechanically changing the elevation view direction of the panels, their beam direction is adjusted (i.e., tilted) electronically.
U.S. Pat. No. 6,864,837 to Runyon et al., the disclosure of which is incorporated by reference, describes a vertical antenna for base stations that implements electrical down tilt. Here the electrical tilt is used for purposes different than reducing antenna profile.
U.S. Pat. No. 6,873,301 to Lopez, the disclosure of which is hereby incorporated by reference, describes a flat antenna utilizing an array of sub-arrays contiguously positioned in a diamond-type pattern. This layout is claimed to achieve lower side lobes.